The present invention relates to a novel dot printing wire having a wear-resistant contact attached to the point thereof.
The term "dot printing" as used herein refers to a typing system wherein numerals and characters are composed and typed by a set of small points, i.e. dots, formed on a recording paper by causing selected wires from among several fine wires closely arranged to each other to strike the paper with proper timing through a copying material such as a carbon ribbon. Dot printing requires no provision of a large number of types in advance. In practice, only a small number of wires are needed in dot printing in order to type numerals and characters. Because of this simplicity, dot printing has been widely used in recent years. A variety of printers have been proposed.
According to a typical type of printer, seven wires which are closely arranged in a row in one direction are continuously moved across a very short distance 5 times in a direction perpendicular to the row, and only the required wires corresponding to a character to be typed are struck in each of the five row positions thereby to form dots in the pattern of that character, one desired character is typed by a selected combination of these dots. Similarly, other characters are typed in turn. Ordinarily, in printing a particular character, the order of the wire to be struck in a certain row position is memorized in another apparatus so that the wire strikes dots one after another in a very short time in response to a command from the apparatus. Accordingly, it is possible to type at a high speed of 100 to 200 characters per second.
In order to form a dot, the wire should be fine. In general, the wire has a diameter of about 0.25 to 0.5 mm and a length of about 10 cm. The wire is struck at high speeds and pressures and is used in a bent state in some positions. As a consequence, the wire has been disadvantageous in that it breaks during use in a relatively short time or the working tip or point of the wire, i.e., the contact point with which a copying material or recording paper is contacted, becomes rapidly worn. A variety of proposals have been made to overcome these disadvantages. However, none have been entirely satisfactory.
For example, the material for the wire has heretofore been selected from steel, tungsten, titanium, tantalum, rhenium and tungsten-rhenium alloys. As stated above, these materials have various defects. In order to overcome the above described difficulties, tungsten carbide-cobalt type super hard materials have been proposed. Alternatively, attempts have been made to form a hard coating using such materials as carbides, e.g., tungsten carbide, and nitrides, e.g., titanium nitride, on the point portion of a wire body made of a conventional material.
However, the super hard alloys are somewhat inferior with respect to ductility and tend to break easily. Further, they are difficult to process and work. The coating method is accompanied by the problems of poor adherence of the coating and difficulty in working the coated portion. While these problems have not been solved to a satisfactory extent, a tungsten wire, which is unsatisfactory with respect to wear-resistance, is mainly being used at the present stage of the art.